Spectroscopic characterization of Cr2+ ions in ZnSe/ZnS crystals under visible excitation

Detailed spectroscopic characterization of Cr:ZnSe (Cr:ZnS) crystals under visible excitation into the charge transfer bands of Cr2+ impurities was performed. Middle infrared photoluminescence of Cr:ZnS under this excitation exhibits shorter rise time (similar to 150ns) than that previously observed in Cr: ZnSe (similar to 4-10 mu s). As a result the quantum yield of Cr:ZnS mid-IR photoluminescence under 10ns pulsed 416nm excitation into the charge transfer band was estimated at close to 100%, which contrasts with low (similar to 14%) quantum yield measured in Cr: ZnSe under 532nm pulsed excitation, indicating the possibility of efficient excitation of the upper laser level of Cr:ZnS using this mechanism. The rise time can be caused by cascade relaxation from higher lying levels through the T-3(1) metastable level, producing luminescence in the near-IR. Measurements of the temperature dependence of the middle- and near infrared photoluminescence signals are reported. These values indicated that more efficient pumping of Cr:ZnSe under 532nm excitation can be achieved at temperatures greater than 300 K. Results of high temperature laser experiments supporting this idea are presented.